The prior art has included many prosthetic mechanical heart valves which may be surgically implanted to replace malfunctioning or diseased endogenous anatomical heart valves.
Among the prosthetic mechanical heart valves of the prior art are included a number of "rotatable" valves. These rotatable valves typically comprise an annular valve body having one or more occluder leaflets pivotally mounted within the annular valve body such that the leaflet(s) will open and close in response to hemodynamic forces of the blood. In this regard, the leaflets move back and forth between an open position whereby blood is permitted to outflow through the annular valve body, and a closed position whereby blood is prevented from backflowing through the annular valve body. A needle-penetrable suture ring is mounted about the outer surface of the annular valve body, and is sutured directly to the endogenous valve annulus of the patient-host. After the suture ring has been firmly sutured to the host tissue, the surgeon may manually rotate the valve body to place the occluder leaflets of the valve in their desired orientation prior to completion of the surgical procedure. Thus, it is necessary for the annular valve body to remain freely rotatable within the suture ring, to facilitate such manual rotation of the valve body by the surgeon. If the annular valve body does not freely rotate within the suture ring, it may be necessary for the surgeon to apply excessive pressure or torque to effect the desired rotation of the annular valve body. The application of excessive pressure or torque to the annular valve body carries a risk of: a) damaging the valve; or b) tearing the sutures which hold the suture ring of the annular valve body in affixation to the host tissue.
In view of the risks associated with the application of excessive pressure or torque to the annular valve body, it is desirable for rotatable prosthetic heart valves to be designed such that the amount of pressure or torque required to effect rotation of the annular valve body within the suture ring is consistently within acceptable limits, thereby avoiding any need for the application of excessive pressure or torque during the surgical procedure.
One example of a rotatable prosthetic heart valve of the prior art is described in U.S. Pat. No. 4,892,540 (Villana) and is manufactured and sold in at least some countries of the world as the Sorin Bicarbon.TM. Valve, by Sorin Biomedica S.p.A., Saluggia, Italy. The rotatable prosthetic heart valve of U.S. Pat. No. 4,892,540 (Villana) comprises an annular valve body having a pair of leaflets pivotally mounted therewithin, and an annular suture ring rotatably mounted therearound. An annular suture ring tracking groove is formed in the outer surface of the annular valve body. The suture ring is formed of a rigid inner ring member having an annular tracking rib formed on the inner surface thereof, and a woven or knitted fabric cover. The annular tracking rib of the rigid suture ring member is snap-fit into the annular tracking groove formed in the outer surface of the valve body. In this manner, the engagement of the tracking rib within the tracking groove serves to hold the suture ring in substantially fixed longitudinal position on the valve body, while allowing the suture ring to remain rotatable relative to the valve body. The fabric cover of the suture ring extends partially between the outer surface of the annular valve body, and the adjacent rigid suture ring member. In this regard, a portion of the fabric material is interposed or captured between the outer surface of the annular valve body and the adjacent inner surface of the rigid ring member. As a result, variations in the thickness of the fabric material used in the manufacture of the suture ring may result in variations in the amount of pressure or torque required to effect rotation of the annular valve body within the suture ring. For example, if the fabric used in the manufacture of the suture ring is relatively thin, very little frictional drag will result from the interposition of the fabric between the outer surface of the annular valve body and the inner surface of the rigid suture ring member, thereby allowing the annular valve body to be rotated with minimal force or torque. On the other hand, if the fabric material used in the manufacture of the suture ring is relatively thick, a greater amount of frictional drag will result from the interposition of the fabric material between the outer surface of the annular valve body and the inner surface of rigid suture ring member, thereby causing excessive force or torque to be required to effect rotation of the annular valve body within the suture ring.
In view of the above-explained potential for variations in fabric thickness in the suture rings to result in corresponding variations in the amount of force or torque required to effect rotation of the annular valve body, it is desirable to design alternative constructions for the annular valve body and/or suture ring to minimize the effect of variations in fabric thickness on the amount of pressure or torque required to effect rotation of the valve within the suture ring.